Recentemente soube-se de um programa canadiano para espiar os movimentos de visitantes usando wifi: CSEC used airport Wi-Fi to track Canadian travellers: Edward Snowden documents
Agora apareceu uma App para Android -- Pry-Fi -- que supostamente evita esses ataques. A App parece algo estranha e requer que o telemóvel esteja "rooted", mas se alguém quiser experimentar agradeço comentários:
One solution is shutting off Wi-Fi completely (including the background network scanning, a setting most people don't know about), but you would lose benefits like automatically connecting to known Wi-Fi networks and improved location awareness for your apps. It also does nothing to help the situation for others.
Pry-Fi will prevent your device from announcing all the networks it knows to the outside world, but it will still allow background scanning and automatically connecting to Wi-Fi networks. While you are not connected to a Wi-Fi network, the MAC address will constantly be pseudo-randomized, following a pattern that still makes the trackers think you are a real person, but they will not encounter your MAC address again. This will slowly poison their tracking database with useless information.
When you do connect to a Wi-Fi network, unless you specify otherwise, your MAC address will also be randomized - the same MAC address will not be used the next time you connect to this or any other network.
This is proof-of-concept code, and how for it will go in the future depends on interest and how well it works. It has been tested on several devices and seems to work, but it is very young still. The magic the app does to achieve its purpose is ever subject to changing Android security policies and OEM customizations, so even though it works now, there really is no saying if it will still be possible in future firmwares.
Of course you should also keep in mind that tracking can be done in many ways, and these W-Fi signals are far from the only method in use.
Further details, device compatibility information, FAQ, discussion, etc is all available on XDA-Developers.com here: